Detector To Help In The Search For Elusive Dark Matter Material

November 16, 2012

Image Caption: Shown is a top-down view of the Lawrence Livermore National Laboratory-designed and built copper photomultiplier tube mounting structure, which is a key component of the LUX detector. Credit: LLNL

Nearly a mile underground beneath the Black Hills of South Dakota, scientists from Lawrence Livermore National Laboratory (LLNL) are using a tank to make key contributions to a physics experiment that will look for one of nature’s most elusive particles, “dark matter.”

The Large Underground Xenon (LUX) experiment located at the Sanford Underground Research Facility in Lead, SD is the most sensitive detector of its kind to look for dark matter, which is thought to comprise more than 80 percent of the mass of the Universe. Scientists believe dark matter could hold the key to answering some of the most challenging questions facing physicists in the 21st century. However, dark matter has eluded detection so far.

The researchers from LLNL have been involved with the LUX project since 2008.

“We at LLNL initially got involved in LUX because of the natural technological overlap with our own nonproliferation detector development programs,” said Adam Bernstein, who leads the Advanced Detectors Group in LLNL’s Physics Division. “It’s very exciting to reflect that as a result, we are now part of a world-class team that stands an excellent chance of being the first to directly and unambiguously measure cosmological dark matter particle interactions in an earthly detector.”

LUX is at the cutting-edge of the science and technology of rare event detection, and as such is of direct interest for LLNL and U.S. nonproliferation, arms control and nuclear security missions. According to LLNL, “In particular, cryogenic noble liquid detectors of this kind may allow for improved, smaller footprint reactor antineutrino monitoring systems, with application to the International Atomic Energy Agency reactor safeguards regime.”

Detectors of very similar design, using xenon or argon, have excellent neutron and gamma ray detection and discrimination properties. They may also assist with missions related to the timely discovery and characterization of fissile materials in arms control and search contexts.

Scientists and technicians from LLNL have made important contributions to LUX.

Peter Sorensen, lab staff physicist, has directed the LUX Analysis Working Group, and spent months at the site helping to install the detector. Sorensen has also written numerous peer-reviewed articles on how to perform searches for a range of dark matter candidates using LUX and related detectors.

Another staff physicist, Kareem Kazkaz, is the author of the LUX detector simulation package known as LUXSIM. Kazkaz has directed the Simulations Working Group for the project. The LUXSIM simulation software is uniquely well suited for low background detectors of this kind. Other users in the dark matter and nonproliferation communities have picked up the software to use in their projects.

John Bower and Dennis Carr (now retired) are LLNL technicians who have played key roles in the manufacture and installation of elements of the LUX detector. These elements include building the precision-machined copper photo multiplier tube mounting apparatus.

Gerry Mok, lab safety engineer, has performed detailed calculations demonstrating the safety of the LUX pressurized and cryogenic systems under a range of possible accident scenarios, which was important to the successful safety review of the LUX detector.

Located in the famous former Homestake gold mine, the Sanford Underground Research Facility (Sanford Lab) is owned and operated by the South Dakota Science and Technology Authority. It is supported by the Department of Energy and the DOE’s Lawrence Berkeley National Laboratory.

The LUX detector took three years to build at Sanford Lab in a surface facility. This past July, it was installed in an excavated cavern 4,850 feet underground with nearly a mile of solid rock protecting the sensitive equipment from the cosmic radiation that constantly bombards the surface of the earth. If the detector were on the surface, cosmic radiation would drown out the faint dark matter signals.

The surrounding rock also emits small amounts of natural radiation, which LUX must be protected from as well. The detector was lowered into a very large stainless steel tank — 20 feet tall by 24 feet in diameter. The tank was then filled with more than 70,000 gallons of ultra-pure de-ionized water that will shield the detector from gamma radiation and stray neutrons.